This invention relates to microelectronics and, particularly, to integrated circuits that may be deployed in environments having elevated levels of ionizing radiation.
Ionizing radiation can have deleterious effects on microelectronics, raising design challenges for microelectronics designed for use in aerospace in nuclear power installations, or in nuclear weapons, for example. In aerospace applications, long-term degradation of performance resulting from cumulative exposure over time (total ionizing dose) can result in eventual failure.
A variety of approaches have been proposed for increasing the total radiation dose durability (and thereby the useful life) of microelectronics for environments having high levels of ionizing radiation. These include, for example, selecting semiconductor materials that are more resistant to effects of radiation; building redundancy into the system or the circuits; and shielding the semiconductor package. Such approaches, when effective, may unacceptably add mass, or unacceptably increase size, or impractically raise cost.
In one approach to shielding a packaged semiconductor die from radiation effects, a cap or cover is installed upon or over the package. The effectiveness of the shield depends upon the thickness of the cover or cap, and the material (typically a metal such as aluminum or copper) of which the cap or cover is made. Some semiconductor die packages are hermetically sealed, typically using a surrounding ceramic or a glass ceramic, and in one approach to shielding such packages, a slug of metal having suitable thermal expansion properties (CTE nearly matched to the ceramic or glass ceramic—typically including a specific combination or alloy of metals, such as a particular copper-tungsten) is embedded in the surrounding ceramic. These shields add significant mass and size, and the materials can be costly.